Radiation curing of unsaturated polyester compositions

ABSTRACT

A cold-forming method for forming shapes from a laminate which has a thermosetting resinous core and thermoplastic face sheets is disclosed. The thermoplastic face sheets are of sufficient thickness and strength so that the sandwich containing the thermosetting core between the face sheets may be cold formed into shaped articles and such shape as is imparted to it is retained by the thermoplastic face sheets without substantial external constraint on the shape as the thermosetting core is cured by a catalyst system consisting essentially of a peroxide catalyst in conjunction with high energy radiation.

Lamb et al.

{ 51*March 6, 1973 RADIATION CURING OF UNSATURATED POLYESTERCOMPOSITIONS [75] Inventors: George Edwin Robert Lamb; Dusan CirilPrevorsek; Hendrikus Johan Oswald, all of Morristown, NJ.

[73] Assignee: Allied Chemical Corporation, New

York, NY.

[ Notice: The portion of the term of this patent subsequent to July 14,1987, has been disclaimed.

[22] Filed: Aug. 22, 1969 [21] Appl. No.: 852,459

[52] US. Cl. ..l56/l99, 156/272, 204/l59.15, 264/236 [5 l 1 Int. Cl..B29c 25/00 [58] Field of Search ..l56/272, 199; 204/l59.1l, 159.15,

[56] References Cited UNITED STATES PATENTS Primary Examiner-Benjamin R.Padgett Assistant Examiner-E. E. Lehmann Att0rney-Arthur J. Plantamura Acold-forming method for forming shapes from a laminate which has athermosetting resinous core and thermoplastic face sheets is disclosed.The thermoplastic face sheets are of sufficient thickness and strengthso that the sandwich containing the thermosetting core between the facesheets may be cold formed into shaped articles and such shape as isimparted to it is retained by the thermoplastic face sheets withoutsubstantial external constraint on the shape as the thermosetting coreis cured by a catalyst system consisting essentially of a peroxidecatalyst in conjunction with high energy radiation.

4 Claims, No Drawings RADIATION CURING OF UNSATURATED POLYESTERCOMPOSITIONS This invention relates to the forming of shaped articlescomprising synthetic thermosetting resins. More particularly, theinvention relates to-the provision of a structure comprising athermosettable plastic lamina which is supported by or sandwichedbetween thermoplastic layers or enclosing face sheets to form acomposite which may be cold-formed into suitable shapes, and to thenovel method of cold-forming shaped articles from said composite andcuring the formed articles free of the shaping apparatus by use of highenergy radiation in combination with a peroxide catalyst.

The concept of preparing shaped articles at ambient temperatures fromlaminates that incorporate thermosetting resins and subsequently curingsaid articles free of external constraint is disclosed in copending US.patent application of Li, et al., Ser. No. 604,255 filed Dec. 23, 1966now US. Pat. No. 3,520,750. The present application is an improvement onthe invention disclosed in said application and discloses in essence anovel method for effecting a relatively more rapid and less costly cureof the thermosetting resin.

The use of high energy radiation to effect various chemical reactions,including polymerization, is known. However, in using high energyradiation for the curing of laminates consisting of a thermoplastic skinand a cross-linkable polymeric core, it is frequently observed that highradiation dosages required for curing the core may lead to severediscoloration of face sheets and/or appreciable deterioration ofmechanical properties. In searching for means which would reduce theradiation dosages required for complete cure of the laminate consistingof acore containing as crosslinkable component, e. g., a mixture ofunsaturated polyester and copolymerizable monomers, we have discoveredthat such an effect can be achieved with unexpected beneficial resultsby the addition of peroxide-type components in the system to beirradiated.

lt is an object of the invention to provide a method for the rapidcuring of shaped articles of thermosetting plastic composition usinghigh energy radiation in conjunction with peroxide catalysts.

It is a more specific object of the invention to provide a novel methodfor the production of thermoset shapes at ambient temperatures usinghigh energy radiation and peroxide catalysts, said method beingcharacterized by a thermosettable layer sandwiched between thermoplasticlayers which are of sufficient strength to permit the desired shapeimparted to the composite to be retained as the thermosettable layer isconverted to the thermoset condition without requiring externalconstraint.

Additional objects and advantages of the present invention will beapparent from the disclosure which follows.

While a variety of curable thermosetting compositions may be utilized inderiving the benefits of the present invention, the use of the processwith unsaturated polyester compositions is especially advantageous.

The term unsaturated polyester is used herein to mean thepolycondensation products of dicarboxylic acids or dihydrides withdihydroxy alcohols when one of the reactants present during thepolycondensation reaction contains non-aromatic unsaturation.Unsaturated polyesters can be modified by thepresence in thepolycondensation reaction mixture of monocarboxylic acids, monohydroxyalcohols, and small amounts of polycarboxylic acids or polyhydroxyalcohols. Unsaturated polyesters most frequently used are obtained byesterifying saturated dihydric alcohols such as ethylene glycol,diethylene glycol, triethylene glycol, trimethylene glycol, a-propyleneglycol, and 1:3-butylene glycol with a-unsaturated a,B-dicarboxylicacids such as maleic, fumaric, itaconic, and citraconic acids. This typeof unsaturated polyester resin may be modified by replacing some ofthe'unsaturated dibasic acids with an equivalent quantity of anotherdicarboxylic acid such as, for example, succinic, adipic, sebacic,phthalic or azelaic acid. Examples of unsaturated monomers capable ofcopolymerizing with the abovedescribed types of unsaturated polyestersare styrene, methyl methacrylate, ethylene glycol dimethacrylate, ethylacrylate, acrylonitrile, vinyl acetate, diallyl phthalate, diallylmaleate, and triallyl cyanurate.

A wide range of peroxide catalysts may be incorporated in the curableresin. As such, for example, are benzoyl peroxide, dicumyl peroxide,t-butyl perbenzoate, t-butyl peracetate, t-butyl hydroperoxide,ditert.-butyl peroxide, t-butyl-cumyl peroxide, diacetyl peroxide,2,5-dimethyl-2,S-dihydroperoxyhexane, 2-ethoxy-2-(t-butyl-peroxy)-ethane, 3,5,5-trimethyl-3- hydroxyl,2-dioxolane, 3 ,5 ,5-trimethyl-3 (t-butylperoxy)-l,2-dioxolane,phthalic peroxide, succinic peroxide, benzoyl acetic peroxide, fatty oilacid peroxides, e.g., coconut oil, acid peroxides, lauric peroxide,stearic peroxide, and oleic peroxide, and terpene oxides, e.g.,ascaridole.

The peroxide compounds are used in amounts ranging from about 0.05percent to about 12 percent by weight based on the total weight of thepolymeric composition and preferably in amounts of from about 0.1percent to about 8 percent by weight. It is an essential feature of thisinvention that the peroxides employed be effective under the influenceof the high energy radiation, such as high energy electrons, attemperatures below the activation temperature recommended for theconventional heat-curing process.

The reactions induced in polymers by radiation (or polymerizationreactions similarly induced) can be effected by means of either gamma orbeta rays. The former are obtained as emanations from a radioactivesubstance such as the isotope cobalt 60 while the latter being highenergy electrons are generally produced by a suitable accelerator. Whilethere is in theory no limit to the dosage of radiation obtainable witheither method, since the dosage is proportional to the time of exposureto the radiation, in practice, the higher energy flux of the beamobtained with an electron accelerator makes this the preferred means incommercial application. Dosages of several megarads can be obtained intimes of a few seconds with such an accelerator, and dosages of thismagnitude can, in fact, be employed for the rapid cure of, for example,mixtures of unsaturated polyesters and styrene.

The advantages of the use of compounds that reduce the radiation dosagefor curing are obvious. The reduced discoloration can eliminate costlypainting of the cured items and/or other finishing operations. Itreduces the time of curing which further improves the economics of theprocess. Furthermore, the fact that the outer thermoplastic sheets arenot severely affected by radiation leads to an over-all improvement inthe mechanical properties of the cured composite.

The following examples are illustrative for this invention. It should beunderstood that the use of peroxidetype additives is not restricted onlyto the laminates of the invention mentioned above, but should beconsidered applicable to any polyester resin system which is curable byhigh energy radiation. Parts are parts by weight unless otherwiseexpressed.

EXAMPLE 1 A viscous liquid whose composition was 27 parts styrene 73parts of a relatively high molecular weight polyester resin having aweight average molecular weight of 160,000 and an acid number of 12.5,prepared by reacting the following components:

propylene glycol 1.05 mol phthalic anhydride 0.5 mol maleic anhydride0.5 mol glycerol 0.01 mol 3 parts benzoyl peroxide was placed betweenparallel thermoplastic sheets lined with aluminum foil. The sandwich wasirradiated with one-half megarad of B-radiation. The foil andthermoplastic sheet were peeled from the cured composition, which had atensile moldulus of 30,100 psi. A similar composition made in identicalmanner but with no benzoyl peroxide had a tensile modulus of 2,550 psi.

EXAMPLE 2 A viscous liquid whose composition was 27 parts styrene 73parts of a relatively high molecular weight polyester resin having aweight average molecular weight of 160,000 and an acid number of 12.5prepared by reacting the following components:

propylene glycol 1.05 mol phthalic anhydride 0.5 mol maleic anhydride0.5 mol glycerol 0.01 mol 1 part of benzoyl peroxide was placed betweenparallel thermoplastic sheets lined with aluminum foil. The sandwich wasirradiated with one megarad of fi-radiation. The foil and sheet werepeeled from the cured composition, which'had a tensile modulus of 25,190psi. A similar composition made in identical manner but with no benzoylperoxide had a tensile modulus of 12,370 psi.

EXAMPLE 3 A viscous liquid whose composition was 27 parts styrene 73parts of a relatively high molecular weight polyester resin having aweight average molecular weight of 160,000 and an acid number of 12.5prepared by reacting the following components:

propylene glycol 1.05 mol phthalic anhydride 0.5 mol maleic anhydride0.5 mol glycerol 0.01 mol 3 pans of benzoyl peroxide psi.

EXAMPLE 4 A viscous liquid composition of 27 parts of styrene 73 partsof a relatively high molecular weight polyester resin having a weightaverage molecular weigl'rt of 160,000 and an acid number of 12.5prepared by reacting the following components:

propylene glycol 1.05 mol phthalic anhydride 0.5 mol maleic anhydride0.5 mol glycerol 0.01 mol 1 part dicumyl peroxide was placed betweenparallel sheets of a thermoplastic material lined with aluminum foil.The sandwich was irradiated with 1 megarad of B-radiation. The foil andthermoplastic sheets were peeled from the cured composition, which had atensile modulus of 17,260 psi. A similar composition made in identicalmanner but with no dicumyl peroxide had a tensile modulus of 12,360 psi.

It will be apparent that various modifications may be effected in theinvention by those skilled in the art without departing from the scopeor spirit of the invention. The several details disclosed asillustrative should not be construed as placing limitations on theinvention except as required by the appended claims.

We claim: 7

l. A method of forming a synthetic resinous thermosettable laminatecomposite comprising sandwiching a thermosetting lamina between outerlaminae of thermoplastic resin, said composite being of sufficientrigidity to retain the shape imparted to said composite, shaping saidcomposite in a forming apparatus at ambient temperature to the desiredshape, said composite being retained in the forming apparatus for aperiod of time sufficient to shape the thermoplastic layers into thedesired shape, removing the shape from the forming apparatus with thethermosetting lamina in a substantially uncured condition, and curingthe thermosetting lamina of said composite with the aid of a perioxidecatalyst and high energy radiation while said shape is free of externalconstraint.

2. The method of claim 1, wherein said thermosetting lamina comprises anunsaturated polyester.

3. The method of claim 1, wherein said thermosetting lamina comprises anunsaturated polyester together with a copolymerizable monomer having aomo

1. A method of forming a synthetic resinous thermosettable laminatecomposite comprising sandwiching a thermosetting lamina between outerlaminae of thermoplastic resin, said composite being of sufficientrigidity to retain the shape imparted to said composite, shaping saidcomposite in a forming apparatus at ambient temperature to the desiredshape, said composite being retained in the forming apparatus for aperiod of time sufficient to shape the thermoplastic layers into thedesired shape, removing the shape from the forming apparatus with thethermosetting lamina in a substantially uncured condition, and curingthe thermosetting lamina of said composite with the aid of a perioxidecatalyst and high energy radiation while said shape is free of externalconstraint.
 2. The method of claim 1, wherein said thermosetting laminacomprises an unsaturated polyester.
 3. The method of claim 1, whereinsaid thermosetting lamina comprises an unsaturated polyester togetherwith a copolymerizable monomer having a group.